The present invention relates to a trephine for component removal in total hip arthroplasty. More particularly, the invention relates to a flexible trephine for removal of bowed prosthesis components.
Removing well-fixed femoral components, particularly cementless components, in revision total hip arthroplasty is often required for recurrent hip instability, sepsis or mechanical failure. If the cementless femoral component is of a fully porous-coated design that has obtained distal osseointegration in the femoral isthmus and diaphysis, then the implant must be transected with a metal cutting device (not illustrated) at the junction of the proximal tapered portion and the distal cylindrical portion. Once transected, the proximal portion is removed from the femur. Then, a rigid, hollow, cylindrical trephine (not illustrated), which is rotated manually or by a machine, is used to disrupt the component-bone interface and remove the distal stem. That is, the trephine is fitted in a coaxial fashion over the stem while being rotated and urged in the longitudinal direction to remove bone and separate the stem from the femur.
Recently, a variety of bowed, fully-porous coated stems 414 for femoral prosthesis components 412 have become available to accommodate the anatomic bow of the femoral canal in the sagittal plane. See FIG. 4. These stems 414 are useful in situations where proximal bone loss is present and distal fixation is required in the femoral diaphysis where the bowed shape of the femur 422 would often prove a difficult match for a straight stem. Bowed implant stems 414 are being used with increasing frequency. Unfortunately, there are currently no proven methods for removing a well-fixed bowed fully porous-coated stem, as the currently available cylindrical trephines are straight (linear) and non-flexible and would fail to progress distally over a bowed implant 412. The difficulty of removing bowed implants 412 discourages their use by some surgeons.